Black-and-white silver halide photographic elements are typically processed in aqueous alkaline developing solutions containing a dihydroxy-benzene developing agent, such as hydroquinone. While development processes based on the use of hydroquinone generally provide very good sensitometric results, they are disadvantageous with regard to ecological and environmental considerations. In particular, hydroquinone and its derivatives, and the oxidized forms thereof, have become of increasing concern in recent years from the point of view of potential toxicity and environmental pollution. Thus, there is an urgent need in the art for a free of hydroquinone development process which produces the same good results of the known development process containing hydroquinone, but which is environmentally more advantageous.
Developing solutions free of hydroquinone and using ascorbic acid developing agents have been used heretofore in a wide variety of photographic developing processes. Thus, for example, developing compositions containing ascorbic acid developing agents have been disclosed in U.S. Pat. Nos. 2,688,548; 2,688,549: 3,922,168; 3,942,985; 4,168,977; 4,478,928; 4,650,746 and 4,975,354.
Recently, several patents have been disclosed on the subject. U.S. Pat. No. 5,098,819 describes a photographic developer composition comprising a developer selected from the group consisting of ascorbic acid and its sugar-type derivatives, their salts and mixture thereof, together with a sulfite, an alkali metal carbonate and a 3-pyrazolidone developer compound.
U.S. Pat. No. 5,147,767 discloses an environmentally-safe, non-toxic non-hydro-quinone and non-alkali metal hydroxide containing photographic developer composition comprising a developer selected from the group consisting of 2-keto gluconic acid and derivatives thereof, together with a sulfite, an alkali metal carbonate and a 3-pyrazolidone developer compound.
WO 93-11,456 discloses a system for rapid access processing of photographic silver halide elements comprising, in combination, a photographic silver halide element of the type containing a hydrazine compound and a developer solution comprising at least one ascorbic acid developing agent selected from the group consisting of ascorbic acid, derivatives thereof and salts of either.
U.S. Pat. No. 5,236,816 describes a photographic developing solution which is free of dihydroxybenzene developing agents, has a pH in the range of from 9.5 to 11.5 and comprises (1) and ascorbic acid developing agent, (2) an auxiliary super-additive developing agent and (3) a carbonate buffering agent in a concentration of at least 0.5 molar. The developing solution is particularly useful in a process for forming a high contrast image in the graphic arts field utilizing a silver halide photographic element comprising a hydrazine compound which functions as a nucleating agent and an amino compound which functions as an incorporated booster. Said developing solution is not particularly useful when a non-nucleated film, for example a radiographic film must be developed.
EP 573,700 discloses a process for developing a silver halide photographic material in a continuous automatic way using a developer solution containing an ascorbic acid analogue or derivative and a 3-pyrazolidone derivative as developing agents and replenishing the developer solution with a replenishing composition having a defined pH.
Developing solutions containing ascorbic acid as main developing agent have the advantage of providing an environmentally favorable alternative to the use of developing solutions containing dihydroxybenzene developing solutions. However, said developing solutions containing ascorbic acid as main developing agent have the disadvantage of poor resistance against aerial oxidation and cannot be left in continuous transport automatic processors for several days without undergoing a dramatic decrease in developing activity. In particular, the pH value of developing solutions containing ascorbic acid must be kept under careful control. In addition, an other disadvantage of said developing solutions is that they are useful in the graphic arts film when a high contrast image is to be obtained, while they are not useful in the radiographic field, where a high contrast image is not desired.
Reductone compounds, and more specifically reductic acid and its derivatives, have been described as compounds useful in silver halide photographic materials. For example, U.S. Pat. No. 4,839,258 discloses a super-high contrast negative type silver halide photographic material comprising a support having provided thereon at least one silver halide emulsion layer containing a) a hydrazine derivative, b) a compound selected from reductones and c) a 6-membered heterocyclic compound having at least 2 nitrogen atoms. Useful reductone compounds are, for example, ascorbic acid, reductic acid, dimethyl reductone and the like. The developer composition used to treat this type of material is a standard developing solution for black-and-white development containing hydroquinone compound as primary developing agent.
Reductic acid derivatives are also known as developing agents for silver diffusion transfer processes, as described in U.S. Pat. No. 3,821,000, wherein the process comprises the steps of a) exposing a film unit comprising photosensitive silver halide, b) contacting said exposed film with processing solution containing an a,b-enediol silver halide developing agent, i.e. tetramethyl reductic acid, thereby providing a visible silver image to said unit as a function of the point-to-point degree of exposure thereof, and c) contacting said silver image with a noble metal ion below silver in the Electromotive Force Series of Elements. In addition, U.S. Pat. Nos. 4,386,151, 4,468,448, 4,4468,449, 4,468,450 and 4,468,451 disclose photographic processes and products for forming an image dye from a colorless precursor of a preformed dye image, the dye having a moiety that undergoes cleavage in the presence of silver ion and/or soluble silver complex. The processing composition comprising tetramethyl reductic acid as the only developing agent, an auxiliary developing agent being not present in said developing solution.
U.S. Pat. No. 4,353,974 describes a process for the production of a photographic image which comprises exposing a photographic assembly containing a hydroxypyridone azamethine compound, treating the exposed photographic assembly with an aqueous alkaline processing bath containing silver halide developer and, in the non-latent image areas, allowing the silver halide developer to diffuse to bleach said azamethine compound to form a photographic dye image. The developer may be hydroquinone, aminophenol, pyrazolidinone, ascorbic acid, a mixture thereof, or some more unusual developers such as reductic acid derivatives.
It could be desirable to provide a black-and-white developing solution, useful both in graphic arts and radiographic fields, free of dihydroxybenzene developing agent, and being stable against aerial oxidation.